94 Ford Ranger smoking AC

My father inlaw has a 94 Ford Ranger that had a small problem. We are trying to pin point it for repair. About a month ago he got into it and turned on the ac and smoke blew out the vents for a few seconds. It had an electrical burning smell. The AC still works, so does everything else but occationaly he gets in and starts the car and he gets the smell again. Anyone ever experience this or can help point the problem? That would be great!